X-ray fluoroscopy (XRF) is a technique used to detect elements present in a sample. An X-ray tube is typically used as a source of X-rays directed to the sample. A detector is responsive to the X-rays emitted (e.g., scattered) from the sample. An analyzer processes the output signals produced by the detector and divides the energy levels of the detected X-ray photons into several energy subranges by counts of the number of X-ray photons detected to produce a graph depicting the X-ray spectrum of the sample.
Handheld XRF analyzers are well known. See the applicants' website at www.innov-x-sys.com. See also U.S. Pat. Nos. 6,501,825; 6,909,770; 6,477,227; and 6,850,592. Using a handheld XRF analyzer, an inspector can determine, for example, whether lead is present in paint on a wall in a house, apartment, school, or other building.
In another example, The European Union has issued a directive called RoHs (Restriction on the Use of Certain Hazardous Substances). This directive restricts the use of certain hazardous substances (e.g., chromium) in electrical and electronic equipment. In still another example, a refineries require a certain grade stainless steel to be used including 0.2%-0.4% titanium.
State of the art XRF devices provide sufficient energy resolution, testing times of a few minutes or less, are powered by batteries, and obtain high X-ray count rates. The best available detector technology that can be used in conjunction with a handheld device to achieve good energy resolution, however, is a silicon PiN diode detector typically with Peltier cooling. This specific detector is limited in maximum count rate such that without special primary beam filtering, it cannot meet the required detection limits and precisions in all cases.
Without filtering the X-ray beam from the source, the maximum count rate of the Si PiN detector is often exceeded and low concentrations of elements such as hazardous substances cannot be reliably detected in a sample.
Filters are known in laboratory based XRF systems typically operated by scientists. For handheld XRF systems used by non-scientists, filters are typically not used or require the user to choose the specific filter material to be placed in front of the X-ray source.
Thus, it would be advantageous to have a handheld XRF device which can be reliably used by an inspector in the field to detect the presence of hazardous substances and other substances.